The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Many modern motor vehicle automatic continuously variable transmissions (CVT) utilize controlled hydraulic fluid (for example, transmission oil) to actuate CVT belt and pulleys (or chain and pulleys) to achieve a desired ratio in downsized turbo boosted engines to optimize fuel economy. The control of such hydraulic fluid is achieved by a valve body that directs hydraulic fluid flow to pulley pistons as well as other clutch and brake actuators. The valve body is supplied with pressurized hydraulic fluid from, typically, a gear or vane pump, which is driven by the engine output shaft or the transmission input shaft.
For example, in some configurations, a fixed displacement pump provides fluid flow proportional to engine speed. The pump is often sized to meet hydraulic pressure and volume demands of the transmission at low speed idle engine conditions. Larger diameter higher displacement pumps that meet hydraulic demands of the transmission near engine idle speed often contribute to undesirable transmission spin losses and decrease efficiency of the transmission. A large pump will provide much greater oil flow than what is consumed by the transmission at higher engine speeds, with higher pump power consumption leading to loss in overall transmission efficiency.
Accordingly, the present invention is directed to a pump that improves transmission efficiency while meeting hydraulic demands of the transmission.